Motor vehicles with rear mounted engines are well known, and it is an especially common practice to use transversely mounted rear engines and their associated drive train configurations in passenger buses because of the distinct advantages this arrangement yields. Typically, transversely mounted engine/drive train arrangements positioned rearward of the vehicle's drive wheels give rise to large overhangs which produce a number of significant adverse effects. Large overhangs produce both structural and operating disadvantages and are especially undesirable in smaller buses with low floors.
Known power train configurations of conventional rear wheel drive vehicles with engine/transmission components rearward of the rear axle are of the T-drive and V-drive types. Generally, the T-drive configuration has an engine/transmission assembly with its axis mounted longitudinally (i.e., along the central fore-and-aft axis of the vehicle) with a prop shaft drivably connected to the input shaft of a rear differential gear box. The V-drive configuration has its engine/transmission/angle gear assembly mounted transversely (i.e., orthogonal to the vehicle's longitudinal axis) and rearward of and parallel to the drive axle, with a prop shaft drivably connected to a rear output shaft of an angle gear box and angled into an input shaft of a differential gear box. A major disadvantage of T-drive and V-drive configurations is that they produce extremely long rear overhangs of the vehicle, often times up to ⅓ of the length of the vehicle. Extremely long overhangs create, in prior art systems, a heavy loading situation of the rear axle through high weight and moment loads, and further create the situation where the front steering axle is not sufficiently loaded thereby creating very unsafe operating conditions for braking and steering. Additionally, long overhangs create a too small rear departure angle that reduces ground clearance at the rear of the vehicle.
Although the problems associated with buses having transversely mounted rear engines and drive trains are well known and have received a lot of design effort over the years, the resulting design compromises have produced arrangements that are deficient in ruggedness, simplicity of design, and cost effectiveness in manufacturing and operating.
Descriptions of typical prior art approaches to conventional V-drive and T-drive arrangements may be found in a number of U.S. patents.
U.S. Pat. No. 5,463,915 to Fuehrer et al. is illustrative of a large body of prior art employing a V-drive configuration. A shown best in FIG. 6 therein, the transversely mounted engine 24 provides drive torque to the rear axles 70 via a transmission and a driveshaft 62. It is not uncommon for V-drive arrangements of this type to produce significant overhangs, on the order of 110 inches.
U.S. Pat. No. 2,262,456 to Grater is illustrative of a large body of prior art using the T-drive configuration, as seen best in its FIG. 1. Note that the transverse rear power plant or engine 13 provides drive torque to dual rear traction wheels through a centrally disposed differential and longitudinally disposed propeller shaft 18. T-drive arrangements also typically exhibit large overehangs, on the order of 130 inches.
Additional teachings of related rear mounted vehicle drive train configurations are found in U.S. Pat. No. 4,535,867 to Botar, and U.S. Pat. No. 4,283,966 to Hagin.
While each of these prior art teachings show approaches that function more or less well for its intended purposes, they have not to date provided a clearly better drive train assembly idealy suited for use in buses, especially buses with low floors and high passenger space utilization. It is exactly these needs that the present invention admirably meets.